Magneto-optical signal processor

ABSTRACT

The present invention relates to the optical processing of information using a magneto-optical light modulator to spatially modulate light energy in accordance with the information. The magneto-optical light modulator includes a thin magnetic film having a spatial magnetic pattern in accordance with the information. The light energy is directed to the thin magnetic film to produce variations in the characteristics of the light energy in accordance with the spatial magnetic pattern. After the light energy has been spatially modulated the light energy is further processed using optical lenses so as to produce a desired transform of the spatially modulated light energy.

United States Patentnsn Eschelbach 1 June 12, 1973 [541 MAGNETO-OPTICALSIGNAL 3,224,333 12/1965 Kock ..340/174.l M PROCESSOR 3,229,273 1/1966Baaba ..340/ 174.1 M 3,368,209 2/1968 McGlauchlin ..340/ 174.1 M Inventg sx ffi f gfig 3,500,361 3/1970 Cushner ..340/174.l-M Assigneei TheMagnavox p y, Torrance, Primary Examiner-Terrell w. Fears Calif.Attorney-Smyth, Roston & Pavitt [22] Filed: March 25, 1971 9 ABSTRACT[211 App]' lzslzz The present invention relates to the opticalprocessing Related US. Application Data of information using amagneto-optical light modulator to spatially modulate light energy inaccordance [63] fggg f g f 700395 with the information. Themagneto-optical light modua an one lator includes a thin magnetic filmhaving a spatial magnetic pattern in accordance with the information.[52] 5g The light energy is directed to the thin magnetic film [51] I tCl Gllc 13/04 Gllb 11/10 to produce variations in the characteristics ofthe light [58] -i 340/173 L 174 1 M energy in accordance with thespatial magnetic patl tern. After the light energy has been spatiallymodulated the light energy is further processed using optical [56]References Cited lenses so as to produce a desired transform of the spa-UNITED STATES P ENT tially modulated light energy. 3,196,206 7/1965Griffiths ..-,....340/l74.1M 27 Claims, 11 Drawing Figures 6040/4/01-208 200 g v 212 244 2a; 216/3 210 yea/01 0f 0 L L222 23! 240 252 r v 234I Mfr/a ffI/djfifl 24/ a Gyzrera/ar MAGNETO-OPTICAL SIGNAL PROCESSORThis application is a continuation of Ser. No. 700,395 filed Jan. 25,1968 and now abandoned.

The optical processing of information is a field of use which is greatlyincreasing. There are many advantages to the use of optical processingas opposed to other types of processing systems such as electronicprocessing. For example, with optical processing two spatial degrees offreedom are present which may be used to represent two independentvariables. The optical processing system can operate on both'independentvariables simultaneously. The simultaneous operation on two independentvariables is an improvement over electronic processing systems .sincethe electronic processing systems only have one independent variable.

In addition to the above advantages, optical processing systems includean additional property in that a Fourier transform relationship existsbetween the light amplitude distributions at the front and back focalplanes 'of lenses which may be used in optical processing systems. ThisFourier transform may be used so as to produce variable transformrelationships on the light energy. The benefits which may be obtainedwith the use of optics versus conventional electronics to processelectrical signals is demonstrated by reference to the followingarticles.

Cheatham et al., Optical Filters Their Equivalence to and DifferenceFrom Electrical Networks, 1954 IRE National Convention Record, pp. 6-12Cutrona et al., Optical Data Processing and Filtering Systems, IRETransactions on Information Theory, Vol. IT-6,June 1960 No. 3,pp.386-400 These publications also demonstrate the manner in which theoptical processing systems may be used so as to produce desired types ofoptical processing. For example, optical processing systems may be usedto pro vide cross-correlation, auto-correlation, convolution, spectralanalysis, antenna pattern analysis, match filtering, etc.

Electronic systems for performing the above types of processing exist,but these electronic systems suffer from the disadvantages inherent insystems possessing a single independent variable so that the electronicsystems have one degree of freedom. As indicated above, in the opticalsystem two independent variables are available which gives two degreesof freedom. Thus, the optical systems can readily handle twodimensionaloperations without resort to scanning,

which would be necessary with the electronic system.

Alternatively, in one-dimensional processing with a single varyingparameter, the second dimension may be used to provide a number ofindependent computing channels for varying values of the unusedvariable. In the optical system, the number of independentonedimensional channels is limited only by the number of positions whichmay be resolved across the optical system aperture. The two-dimensionalnature of the -optical processing system may, therefore, be used toprovide a two-dimensional processor or to provide a multichannel singledimensional processor.

For particular types of operations, the use of the optical processor maypermit a considerable simplification of equipment and eliminate thenecessity for bulky systems to perform the operations using electronicprocessing. The major advantages with the use of the optical processingsystems, therefore, stem from the Fourier transform properties ofoptical lenses as indicated above and also because of the ability ofcylindrical lenses to handle the many parallel channels while stillusing reasonably-sized optics.

Although the inherent advantages stemming from the use of opticalprocessing systems have been apparent for many years, optical processinghas not been used to the degree which would have been expected. Theproblems encountered in the optical processing of input information suchas electrical signals centers on the limitations of available'spatiallight modulators. The standard technique for modulating thelight energy is to use photographic film. The photographic film acts asthe spatial light modulator in accordance with the pattern on thephotographic film. For example, if it is desirable to spatially modulatethe light energy in ac cordance with electrical signals, one techniqueis to photograph the line scan output of a cathode ray tube display thatis intensity modulated with the electrical signals. Other types ofspatial light modulators which have been tried, for example, are thoseusing the Sears Debye effect in liquids or solids.

The photographic film technique gives a large time bandwidth product buthas the disadvantage of requiring a time delay to process the filmbefore the signals can be processed. The spatial modulator using theSears-Debye effect have large bandwidths but are limited on theavailable time aperture by the velocity of sound in the material. Thepresent invention is therefore directed tooptical processing systemsusing magneto-optical light modulators so as to spatially modulate thelight energy in accordance with input information and to produce animproved optical processing system.

The magneto-optical light modulators used in the present inventionincorporate a thin magnetic film which has a spatial pattern of magneticinformation in accordance with the input information. The light energyis directed to the thin film so as to spatially modulate the lightenergyin accordance with the spatial pattern of magnetic information on thethin film. ;The light energy may be' either amplitude modulated or phasemodulated in accordance withthe manner in which the magneto opticallight modulator is used. v

The magneto-optical light modulator included in the improved opticalprocessing system of the present invention uses the Kerr magneto-opticaleffect which produces a change of either rotation or amplitude of lightenergy reflected from a ferromagnetic surface in accordance with themagnetic state of the surface. With the longitudinal Kerrmagneto-optical effect, the magnetization is parallel to the plane ofincidence of the polarized light and the light energy experiences.changes in rotation upon the reflection of the light netization of thethin film switches between two discrete states. If the thin film ismagnetized along the hard axis, the magnetization of the thin film maybe changed continuously between two limits. The present inventioncontemplates the use of either type of magnetization.

The optical processor of the present invention uses the magneto-opticalmodulators as explained above and the light energy which is processedmay be either non-coherent or coherent. For example, an ordinaryincandescent light source would produce non-coherent light energy. Theuse of a laser would produce coherent light energy. There are certainadvantages in the use of a coherent system since the use of a coherentsystem allows for the elimination of error terms which are producedduring the optical processing.

As indicated above, the improved optical processing system of thepresent invention uses a magneto-optical light modulator. One specificexample of a magnetooptical light modulator is an optical prism whichhas deposited on one surface a thin film of magnetic material. Amagnetic tape is disposed adjacent to the thin film of magnetic materialand the magnetic states on the magnetic tape induce correspondingmagnetic states in the thin film. The magnetic tape, of course, may bestationary or may be continuously recorded with the desired information.The magnetic tape may be moved relative to the thin film so that theinformation on the thin magnetic film may be varied in accordance withthe continuous recording of the information on the magnetic tape.

A light source is used to direct light energy towards the thin magneticfilm. The light energy may be collimated and passed through a polarizerso as to control the plane of polarization of the light energy which isdirected to the thin magnetic film. The optical prism maximizes theamount of light energy which is reflected from the thin magnetic film.For example, the optical prism and the thin magnetic film may bedesigned so as to produce a total internal reflection of the lightenergy directed towards the thin film.

As the light energy is reflected from the thin film, the spatialmagnetic states on the thin magnetic film produce changes in the lightenergy at the corresponding spatial positions. In the use of themagneto-optical light modulator with longitudinal magnetization themagnetic states produce changes in the rotation of the light energy inaccordance with the magnetic states. However, it is to be appreciatedthat the thin film may be magnetized in a transverse direction so as toproduce changes in amplitude of the light energy. With the longitudinalmagnetization where the light energy is rotated upon the reflection fromthe thin film, the.

the thin magnetic film may be magnetized either along the easy axis orthe hard axis. When the thin film is magnetized along the easy axis, themagnetic states are either in one of two values and the thin filmexhibits essentially a square hysteresis loop. This type ofmagnetization is useful in digital work. When the thin film ismagnetized along the hard axis, the magnetic states vary continuouslybetween two limits so as to produce a continuously varying magneticsignal in accordance with the degree of magnetization.

In the general use of the optical processor of the present invention,the light modulator spatially modulates the light energy in accordancewith the input information and this spatially modulated light energy isthen optically processed using optical lenses. The processing system maybe used so as to produce an additive, subtractive, multiplitive ordivisive function on the light energy. Also more than onemagneto-optical modulator may be used so as to compare or process thelight energy in accordance with more than one spatially varying signal.

As a specific example, the present invention includes an improvedcorrelator which uses a pair of magnetooptical spatial light modulatorsand wherein the correlation is in accordance with amplitude changes ofthe light energy rather than with phase changes. Each light modulator,therefore,,is a complete spatial amplitude light modulator so as tocorrelate the information in accordance with the amplitude changes. Theimproved correlator of the present invention may use either coherent ornon-coherent light energy. When the light energy is coherent, forexample when the light source is a device such as a laser, thecorrelator may include means for eliminating error terms.

The present invention, therefore, is directed to the improved opticalprocessor using the magneto-optical light modulator, as indicated above,and particular examples of the optical processor of the presentinvention may be seen with reference to the following description anddrawings wherein:

FIG. 1 is a magneto-optical spatial light modulator using a non-coherentlight source;

FIG. 2 is a magneto-optical spatial light modulator using a coherentlight source;

FIG. 3 illustrates the magnetization of the netic film along the easyaxis;

FIG. 4 illustrates the magnetization of the thin magnetic film along thehard axis;

FIG. 5 is a general magneto-optical processing thin magsystem using amagneto-optical light modulator and showing the general functions whichmay be performed by the optical processor of the present invention;

FIG. 6 is a non-coherent correlator using spatial amplitude modulationfrom successive surfaces so as to correlate the information recorded onthe successive surfaces;

FIG. 7 is a coherent correlator using spatial amplitude modulation fromsuccessive surfaces so as to correlate the information recorded on thesuccessive surfaces;

FIG. 8 is a general purpose optical signal processor constructed inaccordance with the present invention and illustrating various methodsof processing the optical signal;

FIG. 9 illustrates the longitudinal Kerr magnetooptic effect;

FIG. 10 illustrates the transverse Kerr magneto-optic effect; and

FIG. 11 illustrates the coherent optical correlator of FIG. 7 using thetransverse Kerr magneto-optic effect of FIG. 10.

In FIG. l, a basic non-coherent spatial light modulator is shown. Thespatial light modulator as shown in FIG. 1 uses the longitudinal Kerrmagneto-optical effect but it is to be appreciated and as will beexplained later, the spatial light modulator may also use the transverseKerr magneto-optical effect. In FIG. I a source of light 10, such as anincandescent light source, directs light energy towards a collimatinglens 12 and is passed through a polarizer 14. The polarizer 14 polarizesthe light energy to lie in a particular plane of incidence. The lightenergy then passes through an optical prism 16 and is directed to a thinmagnetic film 18. The optical prism 16 efficiently couples the polarizedlight to the thin magnetic film 18 and provides for a total internalreflection of the light energy directed to the thin film so as tomaximize the light energy reflected from the thin magnetic film.

A magnetic pattern generator 20 spatially modulates the magnetic statesof the thin magnetic film 18. For example, one type of magnetic patterngenerator which may be used is linearly recorded magnetic tape having aspatial pattern of information. If the magnetic tape is maintained in astationary position, the spatial pattern is transferred to the thinmagnetic film so as to produce a fixed pattern of magnetic informationon the thin film in this stationary position. However, the magnetic tapemay be moved so as to produce a time-varying spatial pattern of magneticinformation on the thin film. The magnetic tape pattern generator incombination with the thin magnetic film, may be used as a directreplacement of the photographic film used in the prior artspatial lightmodulators, except that the delay experienced in the processing of thephotographic film is drastically reduced since the only delay in the useof the moving magnetic tape pattern generator is in the transit timebetween the recording position of the information and the readoutposition of the spatial light modulator. It is to be appreciated,however, that other types of light modulators may be used which operatein real time.

As the light is reflected from the thin magnetic film 18, rotations areproduced in the light energy in accordance with the spatial magneticpattern when the thin magnetic film is magnetized in a direction toproduce the longitudinal Kerr magneto-optical effect. It is to beappreciated that thin magnetic film may be magnetized in a direction soas to produce the transverse Kerr magneto-optic effect so as to directlyamplitude modulate the output from the thin magnetic film 18.

In the magneto-optical light modulator shown in FIG. 1, the longitudinalKerr magneto-optical effect is assumed so that the light energy from thethin magnetic film 18 is directed to an analyzer 22. The analyzer 22 isused to convert the spatial changes in rotation of the light energy tospatial changes in intensity of the light energy. The particularintensity of the light energy is in accordance with the relativepositions of the analyzer 22 and the polarizer 14 and these elementsare, therefore, adjusted so as to produce the desired intensity output.It can be seen, therefore, that light energy produced by the source isconverted to a light output having spatially varying intensities inaccordance with the pattern of information on the thin magnetic film 18.

FIG. 2 illustrates a basic coherent light modulator. In FIG. 2, a sourceof light 50, such as a laser, produces a beam of coherent light energy.Since this coherent light energy usually has a fairly narrow beam size,the light energy is directed to a beam expander including an objectivelens 52 which focuses the light through a sheet 54 which contains apinhole 56. The coherent light energy passes from the pinhole 56 and isdirected to a collimating lens 58 to produce an expanded beam ofcollimated coherent light energy.

The expanded collimated beam of coherent light energy is passed througha polarizer 60 so as to polarize the coherent light energy to a desiredplane of incidence. The spatial light modulator includes the opticalprism 62, the thin magnetic film 64 and the magnetic pattern generator66. These elements are substantially identical to the similar elementsshown in FIG. 1. As the light emerges from the prism 62, it passesthrough the analyzer 66. The analyzer 66 is set so as to produce aspatially varying output signal having variations in light intensity inaccordance with the information spatially distributed on the thinmagnetic film 64.

FIGS. 3 and 4 show two types of magnetization of the thin films 18 and64 illustrated in FIGS. 1 and 2. FIG. 3 illustrates the magnetizationinduced in the thin magnetic film along the easy axis. In the easy axismagnetization shown in FIG. 3, the magnetization induced in the thinmagnetic film can only switch between two values, B, and -B,,, withchanges of the inducing field H. The easy axis magnetization, therefore,can produce only two values of rotation of the light energy reflectedfrom the thin magnetic film. Therefore, only two intensity values can beproduced from the light energy which passes from the analyzers 22 and 66shown in FIGS. 1 and 2. The easy axis magnetization produces a curve asshown in FIG. 3 and this type of curve is commonly referred to as asquare hysteresis loop. One advantage with the easy axis magnetizationis that the thin magnetic film exhibits a strong memory since themagnetization must be driven to one of the two positions.

The easy axis magnetization may oftenbe used in spatial processing but alarger percentage of optical processing cannot work with only two valuesof light intensity. It is, therefore, desirable to provide for a spatiallight modulation which produces a continuous change in light intensity.The continuous change in light intensity may be accomplished by usingthe type of magnetization shown in FIG. 4 which magnetization iscommonly referred to as hard axis. For the hard axis magnetization, theinduced magnetization B in the thin film and, therefore, the rotationsproduced in the light energy, are nearly proportional to the inducingfield H until the values of fl is reached. However, between the valuesof fl there is a linear portion which may be used to produce linearchanges in light output from the analyzers 22 and 66. It is to beappreciated that either type of magnetization may be used for the lightmodulators of FIGS. 1 and 2 depending upon the particular type ofoptical processing desired.

FIG. 5 illustrates a generalized form of an improved optical processingsystem using a magneto-optical light modulator. In FIG. 5, a lightsource 100, which may be either coherent or non-coherent, directs lightenergy to a collimating lens 102 to produce a collimated beam of lightenergy. The light energy then passes through a polarizer 104 to polarizethe light energy in a particular desired plane of polarization. It is tobe noted thatthe polarizer shown in FIG. and the polarizers shown in theother figures are used as an aid to allow the visual alignment of theoptical processing systems by observing static patterns by setting theposition of the analyzer for the operating curve extinction point.However, for a-c operations of the optical processing systems, thispolarizer may be removed, thereby providing for an increase in theusable light input to the spatial light modulator.

The spatial light modulator includes an optical prism 106 which supportsa thin magnetic film 108. A magnetic pattern generator 110 produces aspatially varying pattern of magnetic information in the thin magneticfilm 108. The light energy on reflection from the thin magnetic film 108produces rotations in the light energy and the rotations are convertedto variations in light intensity by an analyzer 112. The spatiallyverying light output signal from the analyzer 112 may now be modified bya processing system 114 which may include optical lenses. The processingsystem 114 may perform any of the normal functions such as addition,subtraction, multiplication and division, or combinations of these, soas to process the spatially varying light output signal from theanalyzer 112 in a desired manner.

The output from the processing system 114 is then directed to a detector116. In a sense, the system of FIG. 5 is a computer in that the opticalprocessing in accordance with various arithmetic functions produces acomputation on the spatially varying light output signal from theanalyzer 112. It should also be appreciated that additional magneticpattern generators may be included in the processing system so as toproduce processing such as correlation or match filtering. The opticalprocessor of the present invention is therefore extremely versatile inthat it may operate on the spatially varying output light signal indifferent ways. One particular example of an optical processorconstructed in accordance with the present invention is the improvedcorrelator shown in FIG. 6.

In FIG. 6, a light source 150 produces light energy which is directed toa collimating lens 152. The collimating lens 1'52 produces a collimatedbeam of light energy which is polarized by the polarizer 154. The outputfrom the polarizer 154 is directed through an optical prism 156 to athin magnetic film 158. The spatial pattern of magnetic information onthe thin magnetic film 158 is controlled by a first magnetic patterngenerator 160. The spatially varying light output from the thin film 158is then directed to an analyzer 162. The first spatial light modulator,therefore, consists of the polarizer 154, the thin film 158, the firstmagnetic pattern generator 160, and the analyzer 162, and converts theinput light energy which has been polarized in a particular plane ofincidence into a spatially varying light output. The polarization of thelight output is a function of the angle of the analyzer and the spatialpattern of the light intensity is in accordance with the pattern ofinformation on the thin film 158.

The spatially varying light output from the first light modulator isdirected to a second light modulator including a prism 164, a-thinmagnetic film 166 and a second magnetic pattern generator 168. Since ithas been assumed that the thin magnetic film has been magnetized in adirection to produce the Kerr longitudinal magneto-optical effect, thelight input to the second light modulator must be polarized in the planeof incidence of the thin magnetic film 166. The rotation of the plane ofpolarization of the light energy may be accomplished by a light rotatingdevice such as a soliel compensator which uses two pieces of calcitewith orthogonal optical axes to rotate the light. The amount of rotationis in accordance with the thickness of the soliel compensator. Thefirstpiece of calcite includes two split wedges 170 and 172 and the secondpiece of calcite is a single, rectangular section 174. The thickness ofthe first piece of calcite is variedby moving the wedges 170 and 172relative to each other so as to control the amount of rotation. Thelight energy is, therefore, properly polarized for direction on the thinmagnetic film 166.

The output from the thin magnetic film 166 passes through an analyzer176 so as to produce an output signal which has spatial distribution oflight energy having an intensity in accordance with the correlation ofthe information on the first thin magnetic film 158 and the second thinmagnetic film 166. The correlated output signal from the analyzer 176 iscoupled through an integrating lens 178 to a photodetector 180 so as toproduce an output signal having characteristics in accordance with thecorrelation between the information on the first thin magnetic film 158and the information on the second thin magnetic film 166.

The correlator shown in FIG. 6 has certain advantages over thecorrelator shown in copending application Ser. No. 632,757, filed Apr.21, 1967, in the name of Stanton H. Cushner now US. Pat. No. 3,500,361and assigned to the same assignee as the instant case. In the priorcopending correlator, the correlation was accomplished by the use of twosuccessive thin magnetic films in the light path and the priorcorrelator had to be operated at the polarizer-analyzer extinction pointso as to produce a multiplication and thereby produce a truecorrelation. However, in the correlator shown in FIG. 6 of thisapplication, each thin magnetic film is followed by an analyzer in thelight path so as to produce individual spatial light modulators havingspatially varying light intensities. Therefore, it is possible toproduce multiplication at any operating point of the polarizer-analyzercurve. The advantages of the system of this application are, first, thecorrelation may be used with a coherent light source, as will beexplained with reference to FIG. 7, as well as with the non-coherentlight source, shown in FIG. 6. Second, the magnitude of the availablesignal from the total correlator is greatly increased when operationoccurs away from the polarizer-analyzer extinction point. The system ofFIG. 6, therefore, provides for an increased output signal over thecorrelator shown in the copending application Ser. No. 632,757 filedApr. 21, 1967 now US. Pat. No. 3,500,361.

The system of FIG. 6 has a particular difficulty in that the outputsignal from the integrating lens 178 includes several d-c error terms.Although these d-c error terms may be minimized, it would be desirableto eliminate these error terms completely. The coherent opticalcorrelator of FIG. 7 may be used so as to eliminate the error terms. Thecoherent optical correlator system of FIG. 7 includes a source ofcoherent light 200, such as a laser, which directs light energy throughan objective lens 202. The objective lens focuses light through apinhole 204, and the light passing through the pinhole is then directedto a collimating lens 206. The use of the objective lens 202 and thepinhole 204, in combination with the collimating lens 206, allows forthe expansion of the beam from the laser 200 without losing thecoherency of the light beam.

The expanded beam of light energy from the collimating lens 206 is thendirected through a polarizer 208 so as to adjust the plane ofpolarization. The light from the polarizer 208 passes through an opticalprism 210 which supports a thin magnetic film 212. The magnetic patternon the thin film 212 is controlled by a magnetic pattern generator 214in the same manner as discussed above with reference to FIGS. 1 and 2.The output from the thin film 212, therefore, includes rotations inaccordance with the pattern of information on the thin magnetic film212. The output signal from the thin magnetic film 212 passes through ananalyzer 216 so as to produce a spatially varying light signal havingvariations in intensity in accordance with the pattern of information onthe thin magnetic film 212.

The polarity of the output light signal from the analyzer 216 isadjusted using a rotator such as the soliel compensator. As indicatedabove, the soliel compensator may be constructed of a first split pieceof calcite, which includes two wedges 218 and 220, and a second piece ofcalcite 222. The first piece of calcite may have its thickness adjustedby varying the position of the wedges 218 and 220 so as to rotate theplane of polarization of the output signal from the soliel compensator.

The light output from the first light modulator, after having beenrotated, may now be directed through a first transforming lens 224. Thetransforming lens 224 is used to eliminate the d-c error terms presentin the signal from the first spatial light modulator. The dc error termsmay be eliminated since the image of the first transforming lens is theFourier transform of the output light signal from the first lightmodulator and the transforming lens 224, therefore, produces a frequencyspectrum of the output light signal from the first light modulator inthe image plane. It is, therefore, possible to remove the dc terms byproperly positioning a d-c stop as shown by the stop 226. The desiredlight energy is, therefore, passed whereas the d-c error terms areeliminated. The desired light energy is then passed to a secondtransforming lens 228 which takes the inverse transform of the firsttransforming lens except for the sign and couples the reconstitutedlight energy except for the dc error terms to the second magneto-opticalspatial light modulator.

The second magneto-optical spatial light modulator includes the prism230 which supports a thin magnetic film 232. A second magnetic patterngenerator 234 produces a spatial magnetic pattern of information on thethin magnetic film 232 so as to modulate the light energy in accordancewith the pattern of information. The spatially modulated light energyfrom the second thin magnetic film 232 is a correlation of theinformation from the first thin magnetic film 212 and the second thinmagnetic film 232.

correlation. This varying light signal is then integrated by anintegrating lens 238 and the output from the integrating lens is passedto the photodetector 240 so as to produce an output signal in accordancewith the correlation of the information between the first thin magneticfilm 212 and the second thinmagnetic film 232. Since essentially all ofthe modulated light reaches the second light modulator but theunmodulated light is eliminated through the use of the dc stop 238,there is y no necessity for providing additional means for eliminatingthe d-c error terms. As indicated above, various types of spatial lightmodulators may be used with the system of FIGS. 6 and 7.

FIG. 8 illustrates a general purpose optical signal processor which hascertain elements similar to those shown in FIG. 7 but has additionalelements to provide additional capabilities. In the general purposeoptical signal processor of FIG. 8, a coherent light source such as alaser 300 produces a beam of coherent light energy. The beam of coherentlight energy is directed to a beam expander including an objective lens302, a pinhole 304 and a collimating lens 306. The light energy from thelaser 300 is, therefore, focused by the objective lens 302 through thepinhole 304 and onto the collimating lens 306 so as to produce anexpanded beam of collimated coherent light energy.

The beam of collimated coherent light energy is directed through apolarizer 308 so as to control the plane of polarization of the lightenergy. The polarized light energy is then directed to a first lightmodulator which includes an optical prism 310 supporting a thin magneticfilm 312. A magnetic tape 314 is disposed adjacent to the thin magneticfilm 312 so as to induce in the thin magnetic film 312 magnetic statescorresponding to the magnetic states in the magnetic tape 314. Themagnetic tape may be moved relative to the thin magnetic film 312 so asto produce a time varying spatial distribution of magnetic informationin the thin magnetic film 312.

The magnetic tape 314 may be supplied from a supply reel 316 and takenup by a takeup reel 318. Idler wheels 320 and 322 control the positionof the magnetic tape 314 so that the magnetic tape passes across thethin magnetic film 312. The magnetic tape 314 may be driven by a capstandrive system including a capstan 324 and a pinch roller 326. The speedof the magnetic tape 314 is controlledin accordance with the speed ofrotation of the capstan 324 so that the magnetic tape may be controlledto move at a constant speed across the thin magnetic film 312.

The magnetic states in the thin magnetic film 312 control the rotationof the light energy directed to the thin film 312 at the various spatialpositions. The rotated light energy is then. directed through ananalyzer 328 so as to produce an output signal having variations inintensity at different spatial positions in accordance with the patternof information on the magnetic tape 314. The plane of polarization ofthe output signal from the analyzer 312 may be controlled by a rotatorsuch as a soliel compensator which includes a first element including apair of wedges 330 and 332 and a second element 334. The thickness ofthe pair of elements 330 and 332 is controlled by movement of theseelements so as to produce the desired rotation of the plane ofpolarization of the light energy from the element 334. The light energymay be directed through a first transforming lens 336 which is used toproduce a frequency spectrum of the light energy in the image plane. Ifthere are any d-c error terms in the image plane, these error terms maybe eliminated by a d-c stop 338. The second transforming lens 340 isused so as to reconstruct the image from the first spatial lightmodulator after the error terms have been removed.

The output from the second transforming lens 340 may now be directedthrough an optical prism 342 to a thin magnetic film 344. The spatialpattern of information on the thin magnetic film 344 may be controlledby a fixed piece of magnetic tape 346 or may be controlled by a movingmagnetic tape similar to magnetic tape 314 used with the first spatiallight modulator. Other means as indicated above may also be used so asto induce spatial patterns of information on the thin film 344.Depending upon the spatial patterns of information which are produced onthe thin magnetic film 344, the optical processor of FIG. 8 may be usedto operate as a correlator, filter, or other type of optical processor.For example, the Cheatham et al. and Cutrona et al. articles referred toabove indicate various types of processing which may be accomplishedwith optical processors. The output from the thin magnetic film 344 isthen directed through an analyzer 348 so as to produce an output signalhaving a spatial pattern of light intensity in accordance with theparticular optical processing.

The output signal may be directed as shown through a pair oftransforming lenses 350 and 352. It is to be appreciated that the lenses350 and 352 represent a generalized lens structure which is known in theoptical processing art so as to perform a particular transformoperation. The output from the lens 352 is directed to a detector 354.The detector 354 may be an image dissector, a viewing screen or othertype of light sensor.

The system of FIG. 8 also includes the pull-out prism 356 which is usedto reflect a portion of the light energy. The prism 356 may include ahalf-silvered surface 358 so that a first portion of the light energypasses to the second spatial light modulator and a second portion of thelight energy is reflected to a second detecting system. Since the firsttransforming lens 336 produces a frequency spectrum of the light energy,a viewing screen 360 may be inserted in the image plane so as todirectly view the frequency spectrum of the light energy from the firstlight modulator. In addition to the visual viewing, the light energy maybe focused by a lens 362 to a detector 364 which may be an imagedissector, an image orthocon or other type of detector which produces anoutput signal in accordance with the frequency spectrum of the lightenergy.

It may, therefore, be seen that the system of FIG. 8 is a generalpurpose optical processor which may be used in accordance with knownoptical processing techniques to produce various processing of inputinformation. As shown in FIG. 8, the first and second spatial lightmodulator may be used so that the input information may be correlated,filtered, analyzed, etc., in a desired manner. The present inventionincludes improvements in optical processing and includes the use of amagneto-optical spatial light modulator. The magneto-optical spatiallight modulator allows for a more efficient modulation of the light enegy thereby eliminating the complexity and limitations in the prior artlight modulators.

The preceding embodiments of the invention have been explained with theassumption that the magnetization of thin magnetic film was in adirection to produce the longitudinal Kerr magneto-optical effect whichin turn produces changes in rotation of the light energy. The changes inrotation of the light energy are then converted to changes in intensityof the light energy for further optical processing. FIG. 9 illustratesthis longitudinal Kerr magneto-optical effect. In FIG. 9, the thinmagnetic film 400 represents any of the thin magnetic films shown in thepreceding figures. The plane of incidence of the light energy is shownby the plane 402 and the various polarizers and rotators are used so asto align this plane of incidence. As can be seen in FIG. 9, the plane ofincidence of the light energy is normal to the plane of the thinmagnetic film 400. The particular light energy in the plane of incidence402 directed toward the thin film 400 is represented by the arrow 404.

As indicated above, the light energy represented by the arrow 404 ispolarized in the plane of incidence so that the arrow 404 lies withinthe plane of incidence 402. It is to be appreciated that the lightenergy 404 may be polarized in other planes. For example, the lightenergy may be polarized in a plane perpendicular to the plane ofincidence 404. The thin magnetic film 400 is magnetized in a directionas shown by the arrow 406. As can be seen in FIG. 9, the magnetizationof the thin film 400 is parallel to the plane of incidence 402 and thistype of magnetization produces the longitudinal Kerr magneto-opticaleffect.

Upon reflection of the light energy 404 from the thin film 400, thereflected light includes a reflected component 408 which lies in theplane of incidence 402. In addition, a rotated component 410 is producedin accordance with the Kerr magneto-optical effect and the rotatedcomponent is perpendicular to the plane of incidence 404. The rotatedcomponent 410 is shown to be either in a positive or a negativedirection depending upon the direction of magnetization as shown by thearrow 406. The resultant output signal which is represented by thevector summations of the arrows 408 and 410 is rotated either clockwiseor counterclockwise away from the plane of incidence 420 in accordancewith the direction of the rotated component 410.

The rotation of the light energy is, therefore, in accordance with themagnetization of the thin magnetic film 400 and the direction ofrotation is in accordance with the direction of magnetization. Therotated light energy may now be passed through an analyzer which is setto pass light energy of a particular polarization which is related tothe initial polarization of the light energy so as to produce variationin the intensity of the light energy in accordance with the rotations.Although the longitudinal Kerr magneto-optical efi'ect in combinationwith the polarizer and analyzer produces a satisfactory intensitymodulation of the output light energy, it would be desirable to providefor a direct intensity modulation of the light energy.

Such a direct intensity modulation may be produced by the use of thetransverse Kerr magneto-optical effect as shown in FIG. 10. In FIG. 10,a thin magnetic film 450 again may represent any of the thin magneticfilms shown in the previously described embodiments. The plane ofincidence of the light energy is represented by the plane d52 and, ascan be seen in FIG. 10, the plane of incidence is perpendicular to theplane of the thin magnetic film 450. The light energy impinging on thethin film 450 is polarized within the plane of incidence 452 and may berepresented by the arrow 454. Again, as with FIG. 9, the light energy asrepresented by the arrow 454 is shown to have its polarization withinthe plane of incidence, but the light energy may actually have otherpolarizations.

The thin magnetic film 450 is magnetized in the transverse direction asshown by the arrow 456. As can be seen in FIG. 10, the magnetization isperpendicular to the plane of incidence, as opposed to the parallelmagnetization shown in FIG. 9. When the light energy is reflected fromthe thin film 450, the output light energy includes two components. Afirst reflected component is shown by the arrow 458. This component lieswithin the plane of incidence 452. In addition to the reflectedcomponent, the Kerr magneto-optical component is shown by the arrow 460.Again, in FIG. as with FIG. 9, the Kerr magneto-optical component may bein one of two opposite directions in accordance with the direction ofmagnetization of the thin magnetic film 450 as shown by the arrow 456.The arrow 460 is shown to extend in two directions. In FIG. 10, the Kerrmagneto-optical component 460 lies within the plane of incidence 452.The Kerr magneto-optical component 460, therefore, either adds to orsubtracts from the reflected component 4S8 thereby providing a directintensity change in the output light energy. The use of the transverseKerr magneto-optical effect as shown in FIG. 10, therefore, producesdirect intensity modulations of the output light.

The transverse Kerr magneto-optical effect as shown in FIG. I0 mayactually be used with any of the previously illustrated embodiments ofthe optical processor. As a specific example, the embodiment of FIG. "7directed to a coherent optical correlator is shown in a modified form inFIG. 11 so as to use the transverse Kerr magneto-optical effect. In FIG.11, similar elements have similar reference characters as in FIG. 7. InFIG. II, the laser 200 produces coherent light energy which is directedthrough the objective lens 202. The light energy is focused through thepinhole 204 by the objective lens 202 so as to expand the beam from thelaser 200. The expanded beam is then directed through the collimatinglens 206 so as to produce an expanded beam of collimated coherent lightenergy. The collimated coherent light energy is polarized in aparticular direction by the polarizer 208. The polarized light energy isthen directed through the optical prism 210 so as to impinge on a thinmagnetic film 500. The thin magnetic film 500 is provided with a spatialpattern of magnetic information by a first magnetic pattern generator502. The pattern of magnetic information provided by the first magneticpattern generator 502 on the thin magnetic film 500 is in a transversedirection, as shown in FIG. 10. The light energy reflected from the thinmagnetic film 500, therefore, has intensity modulations in accordancewith the pattern of magnetic information on the thin magnetic film 500.This intensity modulated light energy is then directed to the solielcompensator the thin magnetic film 504.

consisting of the split member including the two wedge elements 218 and220 and the second element 222 so as to produce the desired rotation ofthe light energy.

The output light from the soliel compensator is directed through thetransforming lens 224 so as to produce a frequency spectrum of the lightenergy. The frequency spectrum of the light energy is then filteredusing the d-c stop 226 so as to remove d-c error components and theremaining light components are passed through the second transfonninglens 228 so as to reconstitute the intensity modulated light energy. Theintensity modulated light energy which has the error terms removed isnow directed through the second optical prism 230 to impinge on the thinmagnetic film 504. The thin magnetic film 504 has a spatial pattern ofmagnetic information induced in the thin film 504 by the second magneticpattern generator 506. As with the first magnetic pattern generator 502,the second magnetic pattern generator 506 produces a transversemagnetization of the magnetic pattern of information on The output lightreflected from the thin magnetic film 504, therefore, includes intensitymodulations in accordance with the correlation of the information on thethin magnetic films 500 and 504. This correlated information is passedthrough an integrating lens 238 and is directed to the photodetector 240so as to provide for an output signal in accordance with thecorrelation.

It is to be appreciated that the transverse Kerr magneto-optical effectmay be used with the other embodiments of the invention illustrated inthe various figures. It is also to be appreciated that the correlatorshown in FIG. 11 and the other embodiments of the invention shown in theother figures may be: varied so as to pro vide optical processing of atype other than correlating. For example, the embodiments may bemodified so as to provide for additional filtering after the signal hasbeen transformed or to provide for matched filtering in accordance withspecific patterns induced in a pair of thin magnetic films.

The invention has been described with reference'to particularembodiments, but various adaptations and modifications may be made. Theinvention, therefore, is only to be limited by the appended claims.

Iclairn:

l. A magneto-optical signal processor, including,

a thin film of magnetic material having a hard axis of magnetization anddisposed to provide magnetization along the hard axis,

first means coupled to the thin film of magnetic material for producinga spatial pattern of magnetic information on the thin film in accordancewith the magnetization of the thin film along the hard axis ofmagnetization,

second means forproducing light energy,

third means coupled to the second means for receiving the light energyfrom the second means and for producing a beam of light from the lightenergy and for directingthe beam of lighttoward the thin film to obtainfrom the thin fihn output light containing spatial variations inaccordance with the spatial pattern of magnetic information on the thinfilm,

optical processing means responsive to the spatial variations in theoutput light from the thin film of magnetic material for providing anoptical Fourier transform of the spatial variations of the output light,and

fourth means responsive to the optical Fourier transform of the spatialvariations of the output light for providing at least a portion of animage of said op tical Fourier transform of the spatial variations ofthe output light.

2. The magneto-optical signal processor of claim 1 wherein the secondmeans produces non-coherent light energy.

3. The magneto-optical signal processor of claim 1 wherein the secondmeans produces coherent light energy.

4. A magneto-optical signal processor, including,

a thin film of magnetic material having a hard axis of magnetization anddisposed to provide magnetization along the hard axis when the hard axisprovides linear magnetization,

first means coupled to the thin film of magnetic material for producingsubstantially linear changes in magnetization of the thin film along thehard axis of magnetization to provide a continuous spatial pattern ofmagnetic information on the thin film in accordance with suchsubstantially linear changes in magnetization,

second means for producing light energy,

third means coupled to the second means for receiving the light energyfrom the second means and for producing a beam of light from the lightenergy and for directing the beam of light toward the thin film toproduce output light from the thin film,

fourth means coupled to the thin film to obtain the production ofcontinuous spatial intensity modulations in the output light inaccordance with the continuous spatial pattern of magnetic informationon the thin film,

optical processing means responsive to the continuous spatial intensitymodulations of the output light from the thin film of magnetic materialfor providing an optical Fourier transform of the continuous spatialintensity modulations of the output light, and

fifth means responsive to the optical Fourier transform of thecontinuous spatial intensity modulations of the output light forproviding at least a portion of an image of the Fourier transform.

5. The magneto-optical signal processor of claim 4 wherein the fourthmeans is accomplished by the transverse recording of the spatial patternof magnetic information on the thin film.

6. The magneto-optical signal processor of claim 4 wherein the fourthmeans is accomplished by an analyzer element placed in the path of theoutput light from the thin film.

7. A magneto-optical signal processor, including,

a thin film of magnetic material having a hard axis of magnetization anddisposed to provide magnetization along the hard axis,

first means coupled to the thin film of magnetic material for producingsubstantially linear changes in magnetization of the thin film along thehard axis of magnetization to provide a continuously variable spatialpattern of magnetic information on the thin film in accordance with suchsubstantially linear changes in magnetization,

second means for producing light energy, third means coupled to thesecond means for receiving the light energy from the second means andfor producing a beam of light from the light energy and for directingthe beam of light toward the thin film to obtain from the thin filmoutput light containing continuously variable spatial modulations inaccordance with the continuously variable spatial modulations inaccordance with the continuously variable spatial pattern of magneticinformation on the thin film,

optical processing means responsive to the output light from the thinfilm of magnetic material for providing an optical Fourier transform ofthe continuously variable spatial modulations of the output light, and

fourth means responsive to the optical Fourier transform of thecontinuously variable spatial modulations of the output light forproviding at least a portion of an image of the optical Fouriertransform.

8. The magneto-optical signal processor of claim 7 wherein the opticalprocessing means for providing the optical Fourier transform includes anoptical lens.

9. The magneto-optical signal processor of claim 7 wherein the firstmeans includes recorded magnetic tape which is moved relative to thethin film to induce the continuously variable spatial pattern ofmagnetic information on the thin film.

10. A magneto-optical signal processor, including,

a thin film of magnetic material having a hard axis of magnetization anddisposed to provide magnetization along the hard axis,

- first means coupled to the thin film of magnetic material forproducing a continuously variable spatial pattern of magneticinformation on the thin film along the hard axis of the thin film,

second means for producing coherent light energy,

third means coupled to the second means for receiving the coherent lightenergy from the second means and for producing a beam of coherent lightfrom the light energy and for directing the beam-of coherent lighttoward the thin film to obtain from the thin film output lightcontaining continuous spatial variations in accordance with the spatialpattern of magnetic information on the thin film,

optical processing means responsive to continuous spatial variations ofthe output light from the thin film of magnetic material for providingan optical Fourier tranforrn of the continuous spatial variations of theoutput light, and

fourth means responsive to the optical Fourier transform of thecontinuous spatial variations of the output light for providing at leasta portion of an image of the optical Fourier transform.

1 1. The magneto-optical signal processor of claim 10 wherein theoptical processing means for providing the optical Fourier transformproduces a frequency spectrum.

12. The magneto-optical signal processor of claim 1 1 wherein the fourthmeans includes'means in the path of the optical Fourier transform of thecontinuous spatial variations of the output light to selectivelyintersect a portion of the frequency spectrum to eliminate any d-c errorterms.

13. A magneto-optical signal processor, including,

ing the light energy from the second means and for producing a beam oflight from the light energy and for directing the beam of light towardthe thin film to obtain from the thin film output light containing alinearly variable spatial pattern of magnetic information on the thinfilm in accordance with the linearly varying spatial pattern of magneticinformation on the thin film along the hard axis,

optical processing means responsive to the linearly variable spatialpattern of the output light from the thin film of magnetic material forproviding an optical Fourier transform of the linearly variable spatialpattern of the output light, and

fourth means responsive to the optical Fourier transform of the linearlyvariable spatial pattern of the output light for providing at least aportion of the image of the optical Fourier transform of the outputlight.

14. The magneto-optical signal processor of claim 13 wherein the firstmeans includes recorded magnetic tape located adjacent to the thin filmto induce the linearly variable spatial pattern of magnetic informationon the thin film along the hard axis of magnetization of the thin filmv15. A magneto-optical signal processor, including,

a thin film of magnetic material having a hard axis of magnetization anddisposed to provide magnetization along the hard axis when the hard axispro vides linear magnetization, first means coupled to the thin film ofmagnetic material for recording a continuously variable spatial patternof magnetic information on the thin film along the hard axis ofmagnetization of thin film,

second means for producing light energy,

third means coupled to the second means for receiving the light energyfrom the second means and for producing a beam of light from the lightenergy and for directing the beam of light toward thethin film and forobtaining from the thin film output light containing continuouslyvariable spatial modulations in accordance with the continuouslyvariable spatial pattern of magnetic information on the thin film alongthe hard axis of magnetization of the thin film,

optical processing means responsive to the continuously variable spatialmodulations of the output light from the thin film of magnetic materialfor providing an optical Fourier transform of the continuously variablespatial modulations of the output light, and

fourth means responsive to the optical Fouriertransform of thecontinuously variable spatial modulations of the output light to provideat least a portion of an image of the optical Fourier transform of theoutput light.

16. The magnetowoptical signal processor of claim 15 wherein the firstmeans includes recorded magnetic tape located adjacent to the thin filmto induce the continuously variable spatial pattern of magneticinformation on the thin film along the hard axis of magnetization of thethin film.

17. A magneto-optical signal processor, including,

a thin film of magnetic material having a hard axis of magnetization anddisposed to provide magnetization along the hard axis where the hardaxis provides linear magnetization,

first means coupled to the thin film of magnetic material for producinga transversely polarized spatial pattern of magnetic information on thethin film along the hard axis of the thin film,

second means for producing light energy,

third means coupled to the second means for receiving the light energyfrom the second means and for producing a beam of light from the lightenergy and for directing the beam of light toward the thin film toobtain from the thin film output light containing spatial intensitymodulations in accordance with the transversely polarized spatialpattern of magnetic information on the thin film, and

optical processing means responsive to the spatial intensitymodulations'of the output light from the thin film of magnetic materialfor providing an optical Fourier transform of the spatial intensitymodulations of the output light, and

fourth means responsive to the optical Fourier transform of the spatialintensity modulations of the output light to provide at least a portionof an image of the optical Fourier transform of the output light.

18. The magneto-optical signal processor of claim 17 wherein the opticalprocessing means includes an optical lens to produce the Fouriertransform of the spatial intensity modulations of the output light.

19. A magneto-optical correlator, including,

a first thin film of magnetic material having a hard axis ofmagnetization and disposed to provide magnetization along the hard axiswhere the hard axis provides linear magnetization,

first means coupled to the first thin film of magnetic material forproducing a continuously variable first spatial pattern of magneticinformation on the first thin film along the hard axis,

second means for producing light energy,

third means coupled to the second means for receiving the light energyfrom the second means and for producing a collimated beam of light fromthe light energy and for directing the collimated beam of light towardthe first thin film to produce output light from the first thin film,

fourth means coupled to the first thin film to obtain the production ofcontinuously variable spatial intensity modulations in the output lightin accordance with the continuously variable first spatial pattern ofmagnetic information on the first thin film along the hard axis,

a second thin film of magnetic material having easy and hard axes ofmagnetization and disposed to provide magnetization along the hard axiswhere the hard axis provides linear magnetization,

fifth means coupled to the second thin film for producing a continuouslyvariable second spatial pattern of magnetic information on the secondthin film, the second thin film being responsive to the continuouslyvariable spatial intensity modulations of the output light from thefourth means to correlate the spatial amplitude modulations in theoutput light from the fourth means with the second spatial pattern ofmagnetic information on the second thin film to produce output lightfrom the second thin film in accordance with such correlations, and

sixth means coupled to the second thin film to produce spatial intensitymodulations in the output light from the second thin film in accordancewith the correlation of the first and second spatial patterns ofinformation.

20. The magneto-optical correlator of claim 19 wherein the second meansfor producing light energy produces coherent light energy.

21. A magneto-optical correlator, including,

a first thin film of magnetic material,

first means coupled to thefirst thin film of magnetic material forproducing a first spatial pattern of magnetic information on the firstthin film,

second means for producing light energy,

third means coupled to the second means for receiving the light energyfrom the second means and for producing a collimated beam of light fromthe light energy and with the collimated beam of light directed towardthe first thin film to produce output light from the first thin film,

fourth means coupled to the first thin film to produce spatial intensitymodulations in the output light in accordance with the first spatialpattern of magnetic information on the first thin film,

a second thin film of magnetic material,

fifth means coupled to the second thin film for producing a secondspatial pattern of magnetic information on the second thin film and withthe second thin film responsive to the output light from the first thinfilm to correlate spatial amplitude modulations in the output light withthe second spatial pattern of magnetic information of the second thinfilm to produce output light from the second thin film, and

sixth means coupled to the second thin film to produce spatial intensitymodulations in the output light from the second thin film in accordancewith the correlation of the first and second spatial pattems' ofinformation, means intermediate the first and second thin films and inthe path of the output light from the first thin film to transform theoutput light from the first thin film to produce a frequency spectrum.

22. A magneto-optical correlator, including,

producing a collimated beam of light from the light energy and with thecollimated beam of light directed toward the first thin film to produceoutput light from the first thin film,

fourth means coupled to the first thin film to produc spatial intensitymodulations in the output light in accordance with the first spatialpattern of magnetic information on the first thin film,

a second thin film of magnetic material,

fifth means coupled to the second thin film for producing a secondspatial pattern of magnetic information on the second thin film and withthe second thin film responsive to the output light from the first thinfilm to correlate spatial amplitude modulations in the output light withthe second spatial pattern of magnetic information of sixth meanscoupled to the second thin film to produce spatial intensity modulationsin the output light from the second thin film in accordance with thecorrelation of the first and second spatial patterns of information,means intermediate the first and second thin films and in the path ofthe output light from the first thin film to transform the output lightfrom the first thin film to produce a frequency spectrum, includingmeans in the path of the frequency spectrum to intercept a portion ofthe frequency spectrum.

23. A magneto-optical signal processor, including,

a thin film of magnetic material having easy and hard axes ofmagnetization and disposed to provide magnetization along the hard axiswhere the hard axis provides linear magnetization,

first means coupled to the thin film of magnetic material for producinga longitudinally polarized spatial pattern of magnetic information onthe thin film along the hard axis of the thin film, second means forproducing light energy.

third means coupled to the second means for receiving the light energyfrom the second means and for producing a beam of light from the lightenergy and for directing the beam of light toward the thin film toobtain from the thin film output light containing spatial intensitymodulations in accordance with the longitudinally polarized spatialpattern of magnetic information on the thin film,

optical processing means responsive to the spatial intensity modulationsof the output light from the thin film of magnetic material forproviding an op tical Fourier transform of the spatial intensitymodulations of the output light, and

fourth means responsive to the optical Fourier transform of the spatialintensity modulations of the output light to provide at least a portionof an image of the optical Fourier transform of the output light.

24. The magneto-optical signal processor of claim 23 a first thin filmof magnetic material,

first means coupled to the first thin film of magnetic material forproducing a first spatial pattern of magnetic information on the firstthin film,

second means for producing light energy,

third means coupled to the second means for receiving the light energyfrom the second means and for wherein the optical processing meansincludes an optical lens to produce the Fourier transform of the spatialintensity modulations of the output light.

25. In the magneto-optical correlator set forth in claim 19,

optical processing means responsive to the spatial modulations of theoutput light from the fourth means for providing an optical Fouriertransform of such spatial intensity modulations before such spatialintensity modulations are directed to the second thin film.

26. In the magneto-optical correlator set forth in claim 21 opticalprocessing means responsive to the spatial intensity modulations fromthe fourth means for providing an optical Fourier transform of suchspatial modulations before such spatial intensity

1. A magneto-optical signal processor, including, a thin film ofmagnetic material having a hard axis of magnetization and disposed toprovide magnetization along the hard axis, first means coupled to thethin film of magnetic material for producing a spatial pattern ofmagnetic information on the thin film in accordance with themagnetization of the thin film along the hard axis of magnetization,second means for producing light energy, third means coupled to thesecond means for receiving the light energy from the second means andfor producing a beam of light from the light energy and for directingthe beam of light toward the thin film to obtain from the thin filmoutput light containing spatial variations in accordance with thespatial pattern of magnetic information on the thin film, opticalprocessing means responsive to the spatial variations in the outputlight from the thin film of magnetic material for providing an opticalFourier transform of the spatial variations of the output light, andfourth means responsive to the optical Fourier transform of the spatialvariations of the output light for providing at least a portion of animage of said optical Fourier transform of the spatial variations of theoutput light.
 2. The magneto-optical signal processor of claim 1 whereinthe second means produces non-coherent light energy.
 3. Themagneto-optical signal processor of claim 1 wherein the second meansproduces coherent light energy.
 4. A magneto-optical signal processor,including, a thin film of magnetic material having a hard axis ofmagnetization and disposed to provide magnetization along the hard axiswhen the hard axis provides linear magnetization, first means coupled tothe thin film of magnetic material for producing substantially linearchanges in magnetization of the thin film along the hard axis ofmagnetization to provide a continuous spatial pattern of magneticinformation on the thin film in accordance with such substantiallylinear changes in magnetization, second means for producing lightenergy, third means coupled to the second means for receiving the lightenergy from the second means and for producing a beam of light from thelight energy and for directing the beam of light toward the thin film toproduce output light from the thin film, fourth means coupled to thethin film to obtain the production of continuous spatial intensitymodulations in the output light in accordance with the continuousspatial pattern of magnetic information on the thin film, opticalprocessing means responsive to the continuous spatial intensitymodulations of the output light from the thin film of magnetic materialfor providing an optical Fourier transform of the continuous spatialintensity modulations of the output light, and fifth means responsive tothe optical Fourier transform of the continuous spatial intensitymodulations of the output light for providing at least a portion of animage of the Fourier transform.
 5. The magneto-optical signal processorof claim 4 wherein the fourth means is accomplished by the transverserecording of the spatial pattern of magnetic information on the thinfilm.
 6. The magneto-optical signal processor of claim 4 wherein thefourth means is accomplished by an analyzer element placed in the pathof the output light from the thin film.
 7. A magneto-optical signalprocessor, including, a thin film of magnetic material having a hardaxis of magnetization and disposed to provide magnetization along thehard axis, first means coupled to the thin film of magnetic material forproducing substantially linear changes in magnetization of the thin filmalong the hard axIs of magnetization to provide a continuously variablespatial pattern of magnetic information on the thin film in accordancewith such substantially linear changes in magnetization, second meansfor producing light energy, third means coupled to the second means forreceiving the light energy from the second means and for producing abeam of light from the light energy and for directing the beam of lighttoward the thin film to obtain from the thin film output lightcontaining continuously variable spatial modulations in accordance withthe continuously variable spatial modulations in accordance with thecontinuously variable spatial pattern of magnetic information on thethin film, optical processing means responsive to the output light fromthe thin film of magnetic material for providing an optical Fouriertransform of the continuously variable spatial modulations of the outputlight, and fourth means responsive to the optical Fourier transform ofthe continuously variable spatial modulations of the output light forproviding at least a portion of an image of the optical Fouriertransform.
 8. The magneto-optical signal processor of claim 7 whereinthe optical processing means for providing the optical Fourier transformincludes an optical lens.
 9. The magneto-optical signal processor ofclaim 7 wherein the first means includes recorded magnetic tape which ismoved relative to the thin film to induce the continuously variablespatial pattern of magnetic information on the thin film.
 10. Amagneto-optical signal processor, including, a thin film of magneticmaterial having a hard axis of magnetization and disposed to providemagnetization along the hard axis, first means coupled to the thin filmof magnetic material for producing a continuously variable spatialpattern of magnetic information on the thin film along the hard axis ofthe thin film, second means for producing coherent light energy, thirdmeans coupled to the second means for receiving the coherent lightenergy from the second means and for producing a beam of coherent lightfrom the light energy and for directing the beam of coherent lighttoward the thin film to obtain from the thin film output lightcontaining continuous spatial variations in accordance with the spatialpattern of magnetic information on the thin film, optical processingmeans responsive to continuous spatial variations of the output lightfrom the thin film of magnetic material for providing an optical Fouriertranform of the continuous spatial variations of the output light, andfourth means responsive to the optical Fourier transform of thecontinuous spatial variations of the output light for providing at leasta portion of an image of the optical Fourier transform.
 11. Themagneto-optical signal processor of claim 10 wherein the opticalprocessing means for providing the optical Fourier transform produces afrequency spectrum.
 12. The magneto-optical signal processor of claim 11wherein the fourth means includes means in the path of the opticalFourier transform of the continuous spatial variations of the outputlight to selectively intersect a portion of the frequency spectrum toeliminate any d-c error terms.
 13. A magneto-optical signal processor,including, a thin film of magnetic material having a hard axis ofmagnetization and disposed to provide magnetization along the hard axiswhere the hard axis provides linear magnetization, first means coupledto the thin film of magnetic material for recording a linearly varyingspatial pattern of magnetic information on the thin film along the hardaxis of magnetization of the thin film, second means for producing lightenergy, third means coupled to the second means for receiving the lightenergy from the second means and for producing a beam of light from thelight energy and for directing the beam of light toward the thin film toobtain from the thin film output light containing a Linearly variablespatial pattern of magnetic information on the thin film in accordancewith the linearly varying spatial pattern of magnetic information on thethin film along the hard axis, optical processing means responsive tothe linearly variable spatial pattern of the output light from the thinfilm of magnetic material for providing an optical Fourier transform ofthe linearly variable spatial pattern of the output light, and fourthmeans responsive to the optical Fourier transform of the linearlyvariable spatial pattern of the output light for providing at least aportion of the image of the optical Fourier transform of the outputlight.
 14. The magneto-optical signal processor of claim 13 wherein thefirst means includes recorded magnetic tape located adjacent to the thinfilm to induce the linearly variable spatial pattern of magneticinformation on the thin film along the hard axis of magnetization of thethin film.
 15. A magneto-optical signal processor, including, a thinfilm of magnetic material having a hard axis of magnetization anddisposed to provide magnetization along the hard axis when the hard axisprovides linear magnetization, first means coupled to the thin film ofmagnetic material for recording a continuously variable spatial patternof magnetic information on the thin film along the hard axis ofmagnetization of thin film, second means for producing light energy,third means coupled to the second means for receiving the light energyfrom the second means and for producing a beam of light from the lightenergy and for directing the beam of light toward the thin film and forobtaining from the thin film output light containing continuouslyvariable spatial modulations in accordance with the continuouslyvariable spatial pattern of magnetic information on the thin film alongthe hard axis of magnetization of the thin film, optical processingmeans responsive to the continuously variable spatial modulations of theoutput light from the thin film of magnetic material for providing anoptical Fourier transform of the continuously variable spatialmodulations of the output light, and fourth means responsive to theoptical Fourier transform of the continuously variable spatialmodulations of the output light to provide at least a portion of animage of the optical Fourier transform of the output light.
 16. Themagneto-optical signal processor of claim 15 wherein the first meansincludes recorded magnetic tape located adjacent to the thin film toinduce the continuously variable spatial pattern of magnetic informationon the thin film along the hard axis of magnetization of the thin film.17. A magneto-optical signal processor, including, a thin film ofmagnetic material having a hard axis of magnetization and disposed toprovide magnetization along the hard axis where the hard axis provideslinear magnetization, first means coupled to the thin film of magneticmaterial for producing a transversely polarized spatial pattern ofmagnetic information on the thin film along the hard axis of the thinfilm, second means for producing light energy, third means coupled tothe second means for receiving the light energy from the second meansand for producing a beam of light from the light energy and fordirecting the beam of light toward the thin film to obtain from the thinfilm output light containing spatial intensity modulations in accordancewith the transversely polarized spatial pattern of magnetic informationon the thin film, and optical processing means responsive to the spatialintensity modulations of the output light from the thin film of magneticmaterial for providing an optical Fourier transform of the spatialintensity modulations of the output light, and fourth means responsiveto the optical Fourier transform of the spatial intensity modulations ofthe output light to provide at least a portion of an image of theoptical Fourier transform of thE output light.
 18. The magneto-opticalsignal processor of claim 17 wherein the optical processing meansincludes an optical lens to produce the Fourier transform of the spatialintensity modulations of the output light.
 19. A magneto-opticalcorrelator, including, a first thin film of magnetic material having ahard axis of magnetization and disposed to provide magnetization alongthe hard axis where the hard axis provides linear magnetization, firstmeans coupled to the first thin film of magnetic material for producinga continuously variable first spatial pattern of magnetic information onthe first thin film along the hard axis, second means for producinglight energy, third means coupled to the second means for receiving thelight energy from the second means and for producing a collimated beamof light from the light energy and for directing the collimated beam oflight toward the first thin film to produce output light from the firstthin film, fourth means coupled to the first thin film to obtain theproduction of continuously variable spatial intensity modulations in theoutput light in accordance with the continuously variable first spatialpattern of magnetic information on the first thin film along the hardaxis, a second thin film of magnetic material having easy and hard axesof magnetization and disposed to provide magnetization along the hardaxis where the hard axis provides linear magnetization, fifth meanscoupled to the second thin film for producing a continuously variablesecond spatial pattern of magnetic information on the second thin film,the second thin film being responsive to the continuously variablespatial intensity modulations of the output light from the fourth meansto correlate the spatial amplitude modulations in the output light fromthe fourth means with the second spatial pattern of magnetic informationon the second thin film to produce output light from the second thinfilm in accordance with such correlations, and sixth means coupled tothe second thin film to produce spatial intensity modulations in theoutput light from the second thin film in accordance with thecorrelation of the first and second spatial patterns of information. 20.The magneto-optical correlator of claim 19 wherein the second means forproducing light energy produces coherent light energy.
 21. Amagneto-optical correlator, including, a first thin film of magneticmaterial, first means coupled to the first thin film of magneticmaterial for producing a first spatial pattern of magnetic informationon the first thin film, second means for producing light energy, thirdmeans coupled to the second means for receiving the light energy fromthe second means and for producing a collimated beam of light from thelight energy and with the collimated beam of light directed toward thefirst thin film to produce output light from the first thin film, fourthmeans coupled to the first thin film to produce spatial intensitymodulations in the output light in accordance with the first spatialpattern of magnetic information on the first thin film, a second thinfilm of magnetic material, fifth means coupled to the second thin filmfor producing a second spatial pattern of magnetic information on thesecond thin film and with the second thin film responsive to the outputlight from the first thin film to correlate spatial amplitudemodulations in the output light with the second spatial pattern ofmagnetic information of the second thin film to produce output lightfrom the second thin film, and sixth means coupled to the second thinfilm to produce spatial intensity modulations in the output light fromthe second thin film in accordance with the correlation of the first andsecond spatial patterns of information, means intermediate the first andsecond thin films and in the path of the output light from the firstthin film to transform the output light from the first thin film toProduce a frequency spectrum.
 22. A magneto-optical correlator,including, a first thin film of magnetic material, first means coupledto the first thin film of magnetic material for producing a firstspatial pattern of magnetic information on the first thin film, secondmeans for producing light energy, third means coupled to the secondmeans for receiving the light energy from the second means and forproducing a collimated beam of light from the light energy and with thecollimated beam of light directed toward the first thin film to produceoutput light from the first thin film, fourth means coupled to the firstthin film to produce spatial intensity modulations in the output lightin accordance with the first spatial pattern of magnetic information onthe first thin film, a second thin film of magnetic material, fifthmeans coupled to the second thin film for producing a second spatialpattern of magnetic information on the second thin film and with thesecond thin film responsive to the output light from the first thin filmto correlate spatial amplitude modulations in the output light with thesecond spatial pattern of magnetic information of the second thin filmto produce output light from the second thin film, and sixth meanscoupled to the second thin film to produce spatial intensity modulationsin the output light from the second thin film in accordance with thecorrelation of the first and second spatial patterns of information,means intermediate the first and second thin films and in the path ofthe output light from the first thin film to transform the output lightfrom the first thin film to produce a frequency spectrum, includingmeans in the path of the frequency spectrum to intercept a portion ofthe frequency spectrum.
 23. A magneto-optical signal processor,including, a thin film of magnetic material having easy and hard axes ofmagnetization and disposed to provide magnetization along the hard axiswhere the hard axis provides linear magnetization, first means coupledto the thin film of magnetic material for producing a longitudinallypolarized spatial pattern of magnetic information on the thin film alongthe hard axis of the thin film, second means for producing light energy.third means coupled to the second means for receiving the light energyfrom the second means and for producing a beam of light from the lightenergy and for directing the beam of light toward the thin film toobtain from the thin film output light containing spatial intensitymodulations in accordance with the longitudinally polarized spatialpattern of magnetic information on the thin film, optical processingmeans responsive to the spatial intensity modulations of the outputlight from the thin film of magnetic material for providing an opticalFourier transform of the spatial intensity modulations of the outputlight, and fourth means responsive to the optical Fourier transform ofthe spatial intensity modulations of the output light to provide atleast a portion of an image of the optical Fourier transform of theoutput light.
 24. The magneto-optical signal processor of claim 23wherein the optical processing means includes an optical lens to producethe Fourier transform of the spatial intensity modulations of the outputlight.
 25. In the magneto-optical correlator set forth in claim 19,optical processing means responsive to the spatial modulations of theoutput light from the fourth means for providing an optical Fouriertransform of such spatial intensity modulations before such spatialintensity modulations are directed to the second thin film.
 26. In themagneto-optical correlator set forth in claim 21, optical processingmeans responsive to the spatial intensity modulations from the fourthmeans for providing an optical Fourier transform of such spatialmodulations before such spatial intensity modulations are directed tothe second thin film.
 27. In the magneto-optical correlator set forth inclaim 22, optical processing means responsive to the spatial intensitymodulations from the fourth means for providing an optical Fouriertransform of such spatial modulations before such spatial modulationsare directed to the second thin film.